In the fabrication of electronic devices, semi-conducting silicon material in the form of wafers is most frequently used for forming electronic circuits in a miniature scale. In the processing of electronic wafers, an extremely clean and contaminant-free environment is normally used to ensure that defect-free circuits are formed on the surface of the wafer. Through the various processing steps, either a high vacuum, a high temperature, a hostile chemical environment or the combination thereof must be utilized as the environment for carrying out the processing steps. A high stress is frequently imposed on the wafer during such processing steps. After an electronic wafer is processed in a processing step, the wafer needs to be cleaned and prepared for the next step of process. The cleaning step for the wafer may involve a general cleaning in which a deionized water jet is sprayed on the entire surface of the wafer, or a specific cleaning step for the wafer edge to remove a photoresist coating or a spin-on-glass coating by an edge bead rinse process.
The edge bead rinse process is necessary for removing an edge bead of either a photoresist or a SOG material such that the wafer may be clamped in a future process by a clamp ring without producing particulate contaminants. In an edge bead rinse process, a high pressure water jet is used for impinging on an edge portion of the wafer so that the coating layer may be flushed away. A high stress is imposed on the wafer edge during the edge bead rinse process. The process therefore further contributes to the formation of crazing (frequently defined as micro-cracks) and cracks in a wafer edge. Both defects may present a serious problem for the electronic wafer and the IC circuits built thereupon. For instance, crazing may cause broken circuits in the IC chips, and may develop into cracks eventually if the specific area of the wafer is further stressed. The formation of cracks in a wafer edge also presents the problem that a whole section of the edge portion may be lost.
Traditionally, crack defects in a wafer edge is determined by visual examination under suitable lighting conditions by a process technician. The wafer may be positioned on a wafer platform which may be tilted to any suitable angle to minimize light reflection from the wafer surface which may lead to defects not being detected. The wafer platform may also be rotated at a suitable rotational speed to facilitate the visual examination. The findings of cracks in the wafer edge portion, even though can be performed in a visual examination, is a time consuming and unreliable process.
The detection of crazing or micro-cracks that has not yet developed into a full crack, is more difficult than the detection of cracks. Presently, there is no reliable method or apparatus can be used to perform such detection.
It is therefore an object of the present invention to provide an apparatus that detects crazing and cracks in a wafer edge without the shortcomings or drawbacks of the conventional apparatus.
It is another object of the present invention to provide an apparatus for determining crazing and cracks in a wafer edge that can be used to produce reliable results.
It is a further object of the present invention to provide an apparatus for detecting crazing and cracks that can be operated in an automated manner.
It is another further object of the present invention to provide an apparatus for detecting crazing and cracks in a wafer edge that utilizes an ultrasonic detection unit for detecting crazing.
It is still another object of the present invention to provide a method for detecting crazing and cracks wherein a laser detection unit is utilized to detect cracks.
It is yet another object of the present invention to provide a method for detecting crazing and cracks in a wafer edge by utilizing ultrasonic waves and laser irradiation.
It is still another further object of the present invention to provide a method for detecting crazing and cracks in a wafer edge that functions in a mini-clean room environment without contamination problems.
It is yet another further object of the present invention to provide a method for detecting crazing and cracks in a wafer edge by utilizing a continuous laser source for detecting cracks or missing edge portions in a wafer.